The present invention relates to the laying of rubber products for the manufacture of tires. More precisely, the present invention relates to the manufacture of a tire by winding strips and it relates to the manufacture of semi-finished products in the form of strips.
It is already known that, in order to manufacture a tire of uncured rubber, the laying of all or part of the rubber products may be effected by winding a strip on a manufacturing support. For example, patent application EP 0 264 600 proposes using extrusion of the volumetric type for laying the rubber products with great accuracy. Patent application EP 0 690 229 proposes a volumetric pump used for continuously extruding a strip of uncured rubber with great accuracy.
One well-known problem in the tire industry is that some sulfur-vulcanizable rubber mixes are quite difficult to extrude: the mix has a tendency to crumble, and does not have a smooth surface downstream of the extrusion but rather a granular, bumpy, rough surface which sometimes contains incipient tears. It is difficult to impart an exact, regular form such as a strip to such mixes. This involves difficulties in handling the extruded semi-finished products. This also involves difficulties in laying such products on a raw tire blank during manufacture because the adhesion of such mixes in the uncured state is generally poor.
This is particularly difficult in the technique of winding a strip on a support because, in this case, the extruded rubber sections are quite weak and it is important to be able to extrude strips at high speed in order to be able to lay the necessary volumes of rubber within a suitable time. Now, generally, for a given mix formulation, the more the rate of extrusion and/or of winding on a support is increased, the more the difficulties increase.
The invention proposes forming a strip by first manufacturing a tube which is subsequently flattened.
A first aspect of the invention relates to the laying of a component comprising uncured rubber during the manufacture of a tire, the laying being effected by winding a band on a rotary support having a receiving surface, by a process comprising the following stages:
extruding uncured rubber through a die imparting a tubular section to the extruded uncured rubber to form a rubber tube, the wall of which defines an internal cavity,
flattening the tubular form and thus obtaining a band which is adhered to said receiving surface.
A second aspect of the invention relates to the manufacture of a band of uncured rubber, with addition of a component to the band downstream of an extrusion operation. This may consist of adding fibers. It may consist of adding an additive, in particular a material capable of migrating into uncured rubber. The process comprises the following stages:
extruding uncured rubber through a die imparting a tubular section to the extruded uncured rubber to form a tube of uncured rubber, the wall of which defines an internal cavity,
concomitantly with the extrusion, introducing a material into said tube, in a predefined amount,
flattening the tubular form and thus obtaining a band.
In the examples described below, a rubber tube is extruded using a cylindrical die containing an ovoid which is also cylindrical and of slightly smaller size so as to leave an air gap of revolution between the nozzle and the ovoid. It goes without saying that the cylindrical shape is not limitative, and other forms may be considered, in particular an oval section. The form of revolution is however advantageous for machining parts.
In what follows, different possible applications of the invention are described, in non-limitative manner, which makes it possible to understand the entire scope and all the advantages thereof.